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Synthetic v. Natural Pesticides

June 6, 2007 11:19 pmJune 6, 2007 11:19 pm

I’ve been getting questions about the biochemist Bruce Ames’ work, which I briefly cite in the Findings column as evidence that synthetic pesticides in our diet are a minuscule risk for cancer. So let me elaborate on the work done by him and his colleague, Lois Swirsky Gold, the director of the Carcinogenic Potency Project at Berkeley.

Dr. Ames was one of the early heroes of environmentalism. He invented the widely used Ames Test, which is a quick way to screen for potential carcinogens by seeing if a chemical causes mutations in bacteria. After he discovered that Tris, a flame-retardant in children’s pajamas, caused mutations in the Ames Test, he helped environmentalists three decades ago in their successful campaign to ban Tris — one of the early victories against synthetic chemicals.

But Dr. Ames began rethinking this war against synthetic chemicals after thousands of chemicals had been subjected to his test. He noticed that plenty of natural chemicals flunked the Ames test. He and Dr. Gold took a systematic look at the chemicals that had been tested on rodents. They found that about half of natural chemicals tested positive for carcinogencity, the same proportion as the synthetic chemicals. Fruits, vegetables, herbs and spices contained their own pesticides that caused cancer in rodents. The toxins were found in apples, bananas, beets, Brussel sprouts, collard greens, grapes, melons, oranges, parsley, peaches — the list went on and on.

Then Dr. Ames and Dr. Gold estimated the prevalence of these natural pesticides in the typical diet. In a paper published in 2000 in Mutation Research, they conclude:

About 99.9 percent of the chemicals humans ingest are natural. The amounts of synthetic pesticide residues in plant food are insignificant compared to the amount of natural pesticides produced by plants themselves. Of all dietary pesticides that humans eat, 99.99 percent are natural: they are chemicals produced by plants to defend themselves against fungi, insects, and other animal predators.

We have estimated that on average Americans ingest roughly 5,000 to 10,000 different natural pesticides and their breakdown products. Americans eat about 1,500 mg of natural pesticides per person per day, which is about 10,000 times more than the 0.09 mg they consume of synthetic pesticide residues.

Even though these natural chemicals are as likely to be carcinogenic as synthetic ones, it doesn’t follow that they’re killing us. Just because natural pesticides make up 99.99 percent of the pesticides in our diet, it doesn’t follow that they’re causing human cancer — or that the .01 percent of of synthetic pesticides are causing cancer either. Dr. Ames and Dr. Gold believe most of these carcinogenic pesticides, natural or synthetic, don’t present problems because the human exposures are low and because the high doses given to rodents may not be relevant to humans.

“Everything you eat in the supermarket is absolutely chock full of carcinogens,” Dr. Ames told me. “But most cancers are not due to parts per billion of pesticides. They’re due to causes like smoking, bad diets and, obesity.”

He and Dr. Gold note that “many ordinary foods would not pass the regulatory criteria used for synthetic chemicals,” but they’re not advocating banning broccoli or avoiding natural pesticides in foods that cause cancer in rodents. Rather, they suggest that Americans stop worrying so much about synthetic chemicals:

Regulatory efforts to reduce low-level human exposures to synthetic chemicals because they are rodent carcinogens are expensive; they aim to eliminate minuscule concentrations that now can be measured with improved techniques. These efforts are distractions from the major task of improving public health through increasing scientific understanding about how to prevent cancer (e.g., what aspects of diet are important), increasing public understanding of how lifestyle influences health, and improving our ability to help individuals alter their lifestyles.

The Ames test is simple, elegant, and rapid–for bacterial mutagens, i.e., substances which can cause changes to DNA in bacteria. Testing for human carcinogens is complex, difficult, and slow. While many known carcinogens are in fact mutagens as revealed by the Ames test, the converse is not necessarily true. A substance mutagenic in bacteria may or may not be a human carcinogen. So when Prof. Ames states that “Everything you eat in the supermarket is absolutely chock full of carcinogens,” does he really mean chock full of bacterial mutagens?

ANSWER FROM JOHN: No, he doesn’t mean the ones found mutagenic in his test. He’s referring to the chemicals found to be carcinogenic in tests with rodents.

A problem with Tierney’s postings is that they lead us down the garden path of false dichotomies. Passionate on both currently defined sides fail to see that it is not the question of “natural” vs. “synthetic,” but the question of how do we use our knowledge effectively to solve big practical problems. We are, as a species, populous and very, very powerful, and very capable of damaging large swathes of our environment. We can do this with both “natural” and “synthetic” materials, tools, what have you. We tend to do too much: we make too many highways cars that are too large, we make and use too many too powerful weapons. Our culture seems to emphasize size and quantity among other things as the best show of status. Yet we have the tools to do things better. Science gives us the means to evaluate the risks and benefits of our actions. We simply must cut down the extent of our impact. This might mean using efficient synthetic chemicals in minimally harmful ways instead of spreading boric acid over the planet or driving small hybrids instead of going back to donkey carts. Or it may mean cutting back on antibiotics given cattle but maintaining some use of hormones. Who knows? We need to find out.

I suppose the problem for me is that we know the long-term effects of eating foods in their natural states (i.e., sans synthetic pesticide residue), but we only know what clinical studies tell us about the long-term effects of eating introduced synthetic pesticides. Yes, we should be concerned about the preventive measures for ensuring public health, but synthetic pesticides weren’t invented with that goal in mind. Synthetic pesticides were created to help increase a farmer’s yield. That’s economics. Plus, synthetic pesticides keep the farmer dependent upon them–sort of like making a junkie–ultimately only fattening the wallets of the chemical companies (don’t see any millionaire farmers out there). And I’m not sure we should be entrusting our health to some chemical company’ bottom line.

This IS a topic where both sides tend to wind up shrieking “YOU’RE NOT LISTENING!” at each other.

I want to suggest this may be because- both sides are – not listening.

Absolutely no question that the natural world is full of natural toxins.

They could be dangerous to your health, under some circumstances. Sometimes, too; evolution may have given us ways to detoxify them; that’s certainly true for many creatures.

There is ALSO absolutely no question that synthetic toxins ARE DIFFERENT, in very basic ways, from natural toxins (for a specific example, no natural chlorinated rings have ever been found). That may make their risks different, too. It’s not likely your metabolism includes enzymes that will deal with chemicals unlike any others.

And evolution has not had time to operate for the synthetics.

The key to the noise- money, primarily; billions.

The argument from the synthetic side that “the world will starve!” if we don’t use their products is clearly specious. We’re busily burning as much food as we can, while starvation continues.

No one starves because the world does not have enough food. They starve because the world doesn’t really care.

Sunlight causes cancer, too. Naturally occuring defensive chemicals in plants have co-existed and co-evolved with the creatures that eat them for hundreds of millions of years. We are the lucky beneficiary of that agonizingly slow process. Most synthetic pesticides and industrial chemicals have been introduced within the last 60 years. Insects and microorganisms can be decimated, develop resistance and their populations can recover quickly but we can’t. So we will lose. Industrial agriculture and manufacturing has poisoned the environment, earth, water and air. No amount of spin will absolve us of this fact: Human activities are causing the extinction of species at a faster rate than at any time since the death of the dinosaurs.

Interesting, and I see their point. The problem with synthetic pesticides, though is that they’re new, and that they’re designed to be effective at low concentrations. People have thousands of years of experience eating broccoli, and there’s no evidence that it’s bad for you. In contrast, the leaves of the rhubarb plant have natural pesticides that are very toxic to humans. With new, synthetic pesticides, we just don’t know until we test them. We gained the wisdom about which plants are good to eat and which aren’t over thousands of years (and plenty of sick or dead people). Now, we don’t need to harm people to figure out what chemicals are toxic, as we can do studies with rats and other models to find reasonable doses that won’t cause problems.

Pesticides “fatten the wallets of chemical companies” but we “don’t see any millionaire farmers”???? Well, chemical companies sell a needed product and make a profit on them, which is just fine. And there are many, many millionaire farmers, whose wallets are fattened by the use of pesticides, and that is fine too.

I would be interested to know the bio-accumulative potential of natural vs synthetic pesticides. It would seem to me that natural pesticides may possibly be less persistant in both the human body and the environment than synthetic pesticides. In short- how quickly are these substances rendered less toxic by the body or the natural environment? If not broken down, carcinogenic and other toxic effects can be magnified.

I applaud John’s contrarian nature, but I feel he’s wading into these waters somewhat unprepared. The carcinogenic properties of pesticides are important, but in my mind the real story is about the physiological effects of pesticides. How they interact with our immune systems, and our endocrine systems.

All signs point to synthetic pesticides being *much* more harmful with regard to these systems, so much so that debates over carcinogenic properties are overshadowed.

Matt’s point about the accumulative properties of natural vs synthetic pesticides is also well-taken.

We aren’t “entrusting our health to some chemical company’s bottom line.” As a culture, we may have a more romantic mental picture of the farmer than of the chemical company CEO, but they are both driven by profit. The farmer needs to sell produce just as desparately as the chemical company needs to sell chemicals. As you said, that’s economics. However, economics is not a zero sum game. Just because someone is making money, that doesn’t mean that everyone else is losing out.

I would be interested to know the bio-accumulative potential of natural vs synthetic pesticides. It would seem to me that synthetic pesticides may possibly be less persistent in both the human body and the environment than natural pesticides.

DNA is DNA. Chemically identical whether it is in a bacterium or in a human. Mutagens cause a chemical reaction or replication error in DNA. It is not the original lesion that causes cancer but the effects of changes in the nature or distribution gene products that are produced many generations after the original chemical damage has been replaced by normal DNA bases of the “wrong” sequence. The Ames test is a cheap and reliable first-pass screen. It fails where the mutagenic chemical is not found in the original ingested material but produced by the activity of metabolic processes that are specific to mammals.

There’s also the issue of the much larger size of the human genome and all the “junk DNA” we have, which may not have much immediate effect if mutated (though new research suggests that it is used for something). Testing bacteria is a very conservative test (which is good in some ways, bad in others), because most of their few genes are absolutely crucial for the survival of the bacterium, as contrasted with the many human genes for superficial traits like hair and eye color.

Response to Natural chlorinated compounds. In fact there are plenty of natural chlorinated and halogenated compounds. About 3500 have been identified, including chlorophenols that are used by some beetles as sex pheromones. These compounds were not looked for by ecologists and environmentalist rather they are found primarily in the pharmacutical literature. The tip off was the discovery of bacteria that can de-chlorinate a wide variety of anthropogenic compounds. When researchers looked in un-contaminated pristine areas, these bacteria were also found (thanks to the wonders of molecular biology). If a bacterial type is present , then there must be a substrate. Low and behold, many chlorophenolics were found in things like forest litter. Even one of the earlier antibiotics (Griesiofulvin) was found to contain chlorine and the organism that produced it had a chlorine syntatase enzyme to chlorinate the molecule.

Andrew: Phillip claimed that there were no naturally occuring chlorinated RINGS. Whether that is true or not, I do not know, but you did not refute it.

Something that seemed to be assumed in this article was that pesticides reduce the number of pests. While this seems common-sensical, pesticides can kill off natural predators for the pests and increase pest levels. As pests grow resistant to chemicals, higher levels are needed. Carnivorous predators especially (for example, oviparous spiders of corn ear worm eggs), do not eat plants, and have little resistance to many chemicals, naturally occurring or otherwise.

Once natural predator populations are down, more pesticides must be used, and hence resistance builds up much more quickly, predator populations decline further, and so on and so forth.

Careful research must be done to examine the effect of new pesticides on predators of pests. Unfortunately, much of the research (but by no means all) focuses on what the insecticide does to the pest under consideration: sampling predator populations is time-consuming and difficult.

It is my opinion that excessive pesticide use is driving pest resistance up unnecessarily and causing a frenzied search for new and more exotic pesticides.

Whatever excess rhetoric the Carlson book may have contained, and factual errors it promulgated, the fact remains that some wild bird species were threatened with extinction through DDT use. I am not aware of any other writers of that time that had as significant an impact in alerting the public to this fact, this ecocide.

I would appreciate your thoughts on any other influential ecology writers and what their impact was on saving wild bird populations from insecticides. Below is a quote taken from the EPA on the near extinction of the Bald Eagle from DDT use. The ban of DDT had positive benefits for some endangered species, like the national bird.

Quote: In a national effort to save the iconic bird, the federal government banned the use of DDT in 1972

Here is the CNN piece extract.
Thank You

Bald eagle recovery
Bald eagle populations severely declined in the lower 48 states between 1870 and 1970 due to hunting, habitat loss and the use of DDT.

DDT, a powerful insecticide, made bald eagle eggshells so weak they couldn’t produce viable offspring. In 1963, there were only 417 breeding pairs in the lower 48.

In a national effort to save the iconic bird, the federal government banned the use of DDT in 1972 and placed the bald eagle under protection of the Endangered Species Act, which allowed the government to protect bald eagle habitat. (Learn more about the Endangered Species Act)

These two key factors helped it recover, according to the Fish and Wildlife Service. Today, there are 9,789 breeding pairs in the lower 48 states. (Map: Bald eagles by state)

One landowner ready for delisting is Minnesota retiree Edmund Contoski.

Contoski, 69, wants to build five log homes on his undeveloped seven-acre property along Lake Sullivan. However, the Endangered Species Act has prohibited development within 330 feet of an active bald eagle’s nest on his property — that covers all of Contoski’s usable land.

One theme that comes up in several of the comments is that humans have evolved to deal with natural pesticides, at least in theory. What that overlooks is that plants and their predators battle each other in an ongoing evolutionary arms race. Each generation of plants strives to prevent themselves from being eaten, and each generation of predators strives to prevent itself from starving to death. It’s now thought that sex evolved for that very reason: to provide a shakeup at the molecular level which will confound the organisms enemies. Thus there’s little reason to think that humans have evolved to deal with ever-changing natural pesticides.

The problem with resistance is it will go on since most oraganisms have P-glycoproteins or transporters that are responsible for the resistance. Therefore inorder to keep up with the resistance to pesticides one would have to keep on synthesizing newer pesticides. Unless researchers have gained complete insight into how to turn off P-gp mediated resistance, the best bet probably be to go with synthetic pesticides that are potent at lower concentrations.

Re the Carson book: In 1964 my first job after college was with the Ohio Dept. of Agric. Food lab where I analyzed milk samples for pesticides. Periodically, I would find some DDt, DDE, dieldrin, Aldrin and other clorinated pesticides that farmers were overusing on their hay and feed.

I am certain the Carson book led to funds from the State of Ohio being available for this testing. While DDT later was found not carcinogenic, other chloinated pesticides were. The Carson book did provide the stimulus for curtailing excessive pesticide use and increasing the analzying the carcinogenic properties of “safe” chemicals

“About 99.9 percent of the chemicals humans ingest are natural. The amounts of synthetic pesticide residues in plant food are insignificant…”

While Dr. Ames is a most esteemed researcher, in this area I think he is off base. Lets reword the sentence above and see if we still agree. Replace “synthetic pesticide” with “synthetic hormone” and does anyone think there will be no effects? If only .1% of what you ingest are synthetically created hormones you’ll definitely see results! Barry Bonds hits better thanks to them. People with their thryoid removed stay alive courtesy of them. The point is that just because something is only 1/1000 of what we ingest does NOT mean it can safely be ignored.

Bruce Ames’s theory, which Mr. Tierney clearly supports, that synthetic pesticides aren’t that bad for us is an amazing exercise in compartmentalized and reductionist thinking.

Basically Ames says that synthetic pesticides aren’t that bad for us because there are carcinogens in food, too. He says that just because synthetic pesticides give rats cancer in higher doses doesn’t mean that they make people sick in lower doses.

The fact is that U.S. safety standards for pesticides were developed decades ago as their use pertained to farm crops, not as it pertained to school buildings, homes, or everyone’s lawn and water supply.

Bruce Ames’ theories ignore the current synergistic reality of ubiquitous, long-term, low-level load of small doses of a wide number of chemicals, including synthetic pesticides, anti-microbials, vaccines, and pollutants like diesel exhaust, heavy metals, and fine particle pollution in our air and water, and the effect this load has on our modern human bodies, which are exposed to this cornucopia of chemicals from conception.

Bruce Ames perverts common sense in a false dialectical argument that if we, as a society, seek to avoid exposure to synthetic pesticides we will then ignore the fact that not smoking and healthy eating promotes good health.

That’s just nonsense.

Common sense, life experience, and decades of sound science dictate to me that I have been exposed to enough synthetic chemicals in my life that if I can eliminate synthetic pesticides from my lawn, my home, and my diet, I’m going to be much better off, and that my health is directly affected by the health of the environment I live within.

Once again the natural world has beaten us to the design punch. It does look (to the extent I can tell from a quick perusal) like many natural chlorophenolics are being produced specifically as “weapons” in the microbe wars, yes? And they seem to be uncommon.

All very interesting.

To the extent this clarifies anything – it would seem to further indicate that the entire area is COMPLEX. An area where we might want to change things slowly, and carefully- if at all.

As someone who has taught environmental science at the graduate level, but is not a partner to normal groupthink, let me say that the orginial post is on the money. Further, it is clear to me that most of the commentors HAVE NOT read the papers that the author links to.

My points:
1. The bodies defense mechanics CANNOT distinguish between “natural” and “man-made”. Our defense mechanisms (e.g. cytochrome P450 enzymes) are much better than that, as they had to be, to allow us to survive from an evolutionary standpoint. So, forget about natural v. manmade. Cobra venom is “natural”. Anyone care for a dose?

2. Are there any naturally-occurring chlorinated ring structures? Go out to a forest fire ignited by lightning, and suck some smoke into a tube. If you analyze the smoke you will find dioxins sythesized during the burning of the wood at intermediate burning temperatures. Last time I looked, 2,3,7,8 Tetrachlorodibenzo-p-dioxin was a “natural chlorinated ring” structure. Look it up. And that is but one example off the top of my head.

3. The “endocrine disruptor” stuff is just another example of Crying Wolf. Chemical substances that are not “natural” and are endocrine active are “Xenoestrogens”, and are “endocrine disruptors”. But add flaxseed to your oatmeal in the morning to get “phytoestrogens”? This is totally illogical and not supported by any data. We understand nothing if we do not lump phytoestrogens and xenoestrogens

The false dichotomy of “natural” v. “man-made, or sythetic, or artificial” has created a flat-earth like mountain of ignorance that it will take us 100 years to surmount.

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About

John Tierney always wanted to be a scientist but went into journalism because its peer-review process was a great deal easier to sneak through. Now a columnist for the Science Times section, Tierney previously wrote columns for the Op-Ed page, the Metro section and the Times Magazine. Before that he covered science for magazines like Discover, Hippocrates and Science 86.

With your help, he's using TierneyLab to check out new research and rethink conventional wisdom about science and society. The Lab's work is guided by two founding principles:

Just because an idea appeals to a lot of people doesn't mean it's wrong.

But that's a good working theory.

Comments and suggestions are welcome, particularly from researchers with new findings. E-mail tierneylab@nytimes.com.